Hydraulic and Pollutant Removal Performance of Fine Media Stormwater Filtration Systems

TLDR

Stormwater runoff from urban areas causes hydrologic and ecological problems, and fine media filtration can mitigate these through flow attenuation and pollutant removal. This work assesses the hydraulic and pollutant removal performance of sand‑ and soil‑based stormwater filters at laboratory scale. The study examined how time, cumulative inflow sediment, cumulative water volume, wetting/drying cycles, and compaction affect hydraulic capacity. Hydraulic failure was mainly due to a surface clogging layer; sediment and heavy metals were retained, but soil filters leached nitrogen and phosphorus, with pollutants accumulating in the top 20 % of the filter, so scraping the top 2–5 cm every two years is recommended to prevent failure and heavy‑metal buildup.

Abstract

Stormwater runoff from urban areas has multiple negative hydrologic and ecological impacts for receiving waters. Fine media stormwater filtration systems have the potential to mitigate these effects, through flow attenuation and pollutant removal. This work provides an overall assessment of the hydraulic and pollutant removal behavior of sand- and soil-based stormwater filters at the laboratory scale. The influence of time, cumulative inflow sediment, cumulative water volume, wetting and drying, and compaction on hydraulic capacity was investigated. The results suggested that the primary cause of hydraulic failure was formation of a clogging layer at the filter surface. Loads of sediment and heavy metals were effectively retained; however, the soil-based filters leached nitrogen and phosphorus for the duration of the experimental period. Media pollutant profiles revealed significant accumulation of all pollutants in the top 20% of the filter profile, suggesting that elevated discharges of nutrients was due to leaching of native material, rather than failure to remove incoming pollutants. It is recommended that the top 2–5 cm of the filter surface be scraped off every two years to prevent hydraulic failure; this will also avoid excessive accumulation of heavy metals, which may otherwise have been of concern.